The fact that heat is absorbed or generated at the junction of two dissimilar metals carrying a direct current was discovered by Jean Claude Peltier over a century ago. The direction of current determines the direction of the heat flow toward or away from the junction. In simple terms, a Peltier device (also known as a thermoelectric device) is a heat pump.
Thermoelectric (Peltier) heat pump modules consist, essentially, of a pair of metalized ceramic plates (having high electrical insulation and excellent thermal conductivity properties) between which are sandwiched the desired number of N-type and P-type semiconductor couples. Typical materials used include antimony, lead, bismuth and tellurium. Such modules have been available from a number of manufacturers including MELCOR (Materials Electronic Products Corporation, Trenton, N.J.) for decades. Typically, they have been promoted as performing the same cooling functions as freon based compression or absorption refrigerators and, according to MELCOR, have used or proposed for a wide range of thermal management applications in the following areas:
Military/Aerospace: Inertial guidance systems, military aircraft, electronic equipment cooling, parametric amplifiers, and portable refrigerators. PA0 Laboratory & Scientific Equipment: Infrared detectors, photomultiplier tube housing coolers, lasers, diodes, transistors, integrated circuit coolers, vidacon tube coolers, laboratory cold plates, cold chambers, stir coolers, immersion coolers, ice point reference baths, microtome stage coolers, electrophoresis cell coolers, osmometers, dewpoint hygrometers, air pollution control analyzers, tissue processing refrigerators, oil pour point apparatus, constant temperature baths, and thermostat calibrating baths. PA0 Consumer Products: Recreation vehicle refrigerators, mobile home refrigerators, portable picnic coolers, wine coolers, beer keg coolers, and aquarium coolers. PA0 Mobile Refrigerators: Medical, pharmaceutical, and food service. PA0 Restaurant Equipment: Cream dispensers, butter dispensers, and display case coolers. PA0 Medical Instruments: Hypothermia blanket chillers, opthomological cornea freezers, blood analyzers, and tissue preparation and storage. PA0 Beverage Coolers: Aircraft water coolers, wine coolers, cream dispensers, and beer keg coolers. PA0 U.S. Pat. No. 4,744,220 to J. M. Kerner et al. for an under sink water heating and/or cooling system, with a liquid cooled heat exchanger (see FIG. 4.A.) PA0 U.S. Pat. No. 4,476,685 to J. D. Aid directed to apparatus for heating or cooling blood and blood plasma. PA0 U.S. Pat. No. 4,848,090 to A. C. Peters for maintaining the temperature of an integrated circuit under test. PA0 U.S. Pat. No. 4,922,721 to W. M. Robertson, et al. for a mobile storage compartment with a thermoelectric cooling system. PA0 U.S. Pat. No. 4,823,554 to L. Trachtenberg, et al., directed to a portable thermoelectric heating and cooling food container adopted for use in a vehicle. PA0 U.S. Pat. No. 4,799,358 to U. C. Knopf et al. for a device for cooling and deep freezing samples of a biological material with layered Peltier cooling elements (at least two cooling layers containing blocks of Peltier elements, alternating with plates of heat conducting metal, preferably aluminum). PA0 U.S. Pat. No. 4,764,193 to L. G. Clawson for thermoelectric frost collectors for freezers. PA0 Provide a thermoelectric heating and cooling system in which the load plate includes a hollow metal housing which is filled with a liquid, such as water or mixture of water and ethyl alcohol, which resists rapid changes in temperature to sustain the heating (or cooling, depending on the direction of current through the thermoelectric modules) effect. PA0 Provide a thermoelectric heating and cooling system with metal spacers between the thermoelectric modules and the heat sink to provide an initial heat removal stage before the thermal energy reaches the primary heat sink for final dissipation. PA0 Provide a thermoelectric heating and cooling system where passages are provided for cooling and heating both the metal spacers and the heat sink and wherein such passages are interconnected. PA0 Provide a thermoelectric heating and cooling system with ducts for both the load plate and the heat sink and wherein the ducts are interconnected by an opening such as a venturi. PA0 Reduction of fossil fuel consumption. PA0 Reduction of air pollution. PA0 Reduction of noise pollution. PA0 Reduce and in some cases eliminate use of freon. PA0 Reduction of engine wear and tear and resultant down-time.
Various refrigeration/heating devises using thermoelectric modules are disclosed in a considerable number of U.S. patents including:
U.S. Pat. No. 4,785,637 to R. Giebeler which relates to thermoelectric cooler with improved heat dissipation (see bottom of column 3 and top of column 4).
Despite the fact that the Peltier effect has been known for over a century, to applicants' knowledge thermoelectrics have never been utilized in vehicle cooling systems, which today remain freon based. Even, in the case of truck tractors, where auxiliary heating/cooling systems have been proposed or used when the main engine is off, such auxiliary systems utilize an auxiliary fossil fuel burning engine and the tractors' existing freon based system. See, for instance, U.S. Pat. No. 4,825,663 to P. S. Nijjar.
Auxiliary systems such as disclosed by Nijjar have a number of drawbacks including fossil fuel depletion, use of freon, environmental pollution and engine wear and tear. Environmental pollution includes the release of freon (which seriously damages the ozone layer), hydrocarbons and other exhaust emission pollutants into the atmosphere, and noise pollution.
Thermoelectric based vehicle air conditioning systems (whether truck tractor, truck or passenger car) for selectively heating and cooling the passenger compartment thereof are disclosed in U.S. Pat. No. 4,280,330 to V. Harris et al. and U.S. Pat. No. 3,138,934 to A. E. Roane. The systems disclosed therein are, in applicants' opinion, impractical, probably won't work and have not been commercialized. In the case of Harris et al., there is no mention of the heat leak characteristics of the vehicle in question, or the heat load, or of varying the heating and cooling as to comfort. More importantly, the design of the thermoelectric configuration is not specified, with only a general reference to interior and exterior heat sinks. Further, there is no current limiting circuitry, without which the thermoelectric device or devices (the number is not specified) will run away. Finally, thermoelectrics are linear devices, not digital, and need to operate by linearly increasing or decreasing current, not by using a thermostat which opens and closes a circuit turning the thermoelectric device either off or on. Roane is similarly defective.
Despite the disclosures in these two patents and the numerous other uses/proposed uses for thermoelectric modules, applicants are not aware of any thermoelectric vehicle heating/cooling system which has been commercialized. As indicated above, the designs which applicants' are aware of are impractical and probably won't work. Further, up until now freon has been the refrigerant of choice.
In view of the foregoing, it is the general objective of the present invention to provide a CFC-free air conditioning system that effectively conditions (heats or cools) a given volume of air (such as a room or cab of a truck tractor) to a preselected temperature, maintains the preselected temperature for protracted periods of time, with low electrical power requirements, where the heat generated is rapidly transported from the Peltier junction, and which reduces the drawbacks which result from the transmigration of thermal energy.
It is also the objective of the present invention to:
In the case of vehicle heating/cooling systems, additional objectives include:
These and other objectives are achieved by the invention disclosed and claimed herein.